But the largest bump occurred in the youngest age group, those between 20 and 29 years old. Incident rates in this age range rose 5.2 percent a year in men and 5.6 percent a year in women.
Siegel said more research is needed to identify the underlying cause for the age disparity in colorectal cancer rates.
"We aren't sure exactly what's going on," she said. "But, clearly, I think the increased rates among younger adults, while low, are substantial and need some attention. For now we can say that there is obviously an obesity epidemic going on in the U.S., and so that probably has something to do with it. Also, there has been a change in dietary patterns over the past couple of decades, reflected in an increase in fast-food consumption and red meat consumption among young people."
"But whatever the cause, I would say clinicians should perhaps be more aware of the risks involved when younger people in their 20s and 30s come in with symptoms for what could be colorectal cancer," Siegel added. "This current finding suggests that perhaps clinicians need to act on the risk a little bit more aggressively."
The findings are in the June issue of Cancer Epidemiology Biomarkers and Prevention.
According to American Cancer Society estimates, 106,000 new diagnoses of colon cancer are projected in the United States this year, along with almost 41,000 new cases of rectal cancer. The numbers will include about 15,000 people younger than 50, Siegel noted.
An estimated 50,000 people will die from the diseases combined this year.
Dr. Warren Enker, a colorectal surgeon and vice chairman of surgery at Beth Israel Medical Center in New York City, said that the new analysis "doesn't surprise me in the least."
"A dietary cause makes sense," he said. "If you take kids who are in an environment where the gene
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